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Where do security bugs come from? Any how do you find them in the real world? Stanford CS 155 Spring 2014 Alex Stamos CISO, Yahoo.

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Presentation on theme: "Where do security bugs come from? Any how do you find them in the real world? Stanford CS 155 Spring 2014 Alex Stamos CISO, Yahoo."— Presentation transcript:

1 Where do security bugs come from? Any how do you find them in the real world? Stanford CS 155 Spring 2014 Alex Stamos CISO, Yahoo

2 CISO at Yahoo! founded Artemis Internet (.secure and.trust) 2004 – co-founded iSEC Partners Berkeley BS EECS ‘01 Your humble narrator

3 Who is looking for security bugs? Bug Finding Techniques Sample of real bugs found in the wild Bug Finding as Warfare I’m in love with security; whatever shall I do? Agenda

4 Who looks for security bugs? Engineers Criminals Security Researchers Pen Testers Governments Hacktivists Academics

5 Goals: Find as many flaws as possible Reduce incidence of exploitation Thoroughness: Need coverage metrics At least find low-hanging fruit Access: Source code, debug environments, engineers Money for tools and staff Engineers (create and find bugs)

6 People care about features, not security (until something goes wrong) Engineers typically only see a small piece of the puzzle “OMG PDF WTF” (Julia Wolf, 2010) How many lines of code in Linux ? How many lines in Windows NT 4? How many in Adobe Acrobat? Engineering challenges

7 People care about features, not security (until something goes wrong) Engineers typically only see a small piece of the puzzle “OMG PDF WTF” (Julia Wolf, 2010) How many lines of code in Linux ? 8 – 12.6 million How many lines in Windows NT 4? million How many in Adobe Acrobat? 15 million Engineering challenges

8 Goals: Money (botnets, CC#s, blackmail) Stay out of jail Thoroughness: Reliable exploits Don’t need 0-days (but they sure are nice) Access: Money Blackbox testing Criminals

9 Goals: Column inches from press, props from friends Preferably in a trendy platform Thoroughness: Don’t need to be perfect, don’t want to be embarrassed Access: Casual access to engineers Source == Lawyers Security Researchers

10 Goals: Making clients and users safer Finding vulns criminals would use Thoroughness: Need coverage Find low-hanging fruit Find high impact vulnerabilities Don’t fix or fully exploit Access: Access to Engineers Access to Source Permission Pen Testers

11 Goals: Attack/espionage Defend Thoroughness: Reliable exploits Access: Money Talent Time Governments

12 Goals: Doing something “good” Stay out of jail Thoroughness: Reliable exploits Don’t need 0-days Access: Talent Plentiful targets Hacktivists

13 Goals: Finding common flaws and other general problems Developing new crypto Make something cool and useful Make everyone safer Thoroughness: Depth in area of research Access: Creating new things Blackbox Academics

14 Bug Finding Techniques

15 Black Box Bug Finding Exercise Manual manipulation Fuzzing Process hooking Watch for response Process stalking Debugging Emulation Determine exploitability Disassembly Debugging Basic goal is to exercise all states of software while watching for a response that indicates vulnerability

16 Fuzzing

17 “Smarter Fuzzing” Record or implement path through gating functions Utilize knowledge of protocol or file format Use process hooking

18 Debugging

19 Reverse Engineering Decompilation Often used for semi-compiled code.Net CLR Java Flash Can work with C++ w/ symbols Disassembly 1:1 matching with machine code Modern disassemblers allow for highly automated analysis process Protocol Reverse Engineering

20 Disassembly - IDA Pro

21 Reversing Patches - BinDiff

22 Defeating Black Box Bug Analysis Many programs include anti-debug functionality Check PDB System calls, monitor process space Throw INTs, test for catch Timing tests Anti-Reversing Dynamic Unpacking Pointer Arithmetic Encrypted and obfuscated function calls

23 Anti-Anti-Debug - Snitch

24 Snitch Output on WMP Potential break-point debugger check at 0x4bf9f889 (blackbox.dll) Exception handler 1 is at 0x4bf9fe71 (blackbox.dll) Exception handler 2 is at 0x7c839ac0 (kernel32.dll) Potential break-point debugger check at 0x4bf9f9fc (blackbox.dll) Exception handler 1 is at 0x4bf9fe71 (blackbox.dll) Exception handler 2 is at 0x7c839ac0 (kernel32.dll) Potential break-point debugger check at 0x4bf9f889 (blackbox.dll) Exception handler 1 is at 0x4bf9fe71 (blackbox.dll) Exception handler 2 is at 0x7c839ac0 (kernel32.dll) Potential break-point debugger check at 0x4bf9f889 (blackbox.dll) Exception handler 1 is at 0x4bf9fe71 (blackbox.dll) Exception handler 2 is at 0x7c839ac0 (kernel32.dll) Potential break-point debugger check at 0x4bf9f889 (blackbox.dll) Exception handler 1 is at 0x4bf9fe71 (blackbox.dll) Exception handler 2 is at 0x7c839ac0 (kernel32.dll) Potential OutputDebugString debugger check at 0x7c812aeb Module: \Device\HarddiskVolume1\WINDOWS\system32\kernel32.dll Potential break-point debugger check at 0x4df75f36 (drmv2clt.dll) Exception handler 1 is at 0x4dfda68e (drmv2clt.dll) Exception handler 2 is at 0x7c839ac0 (kernel32.dll)

25 White Box Bug Finding Black Box techniques always work better with more context More quickly triage flaws Patch flaws much faster Analysis can start with source code Look at sensitive areas Use lexical analysis to give pointers Flawfinder RATS Use semantic analysis Coverity Fortify Most White Box techniques also increase false positive count

26 All are looking for the similar things: vulnerable systems Let’s dive in and look at vulns that we all look for Overall Goals

27 Sample of bugs found in the wild by us

28 Wild bug 1: (session management)

29

30

31 Sellers can post/modify goods PostItem(description, price): sellers post items ModifyPrice(itemID, newPrice): used by sellers to modify item prices Buyers can purchase goods ViewItem(itemID): used by the web app when potential buyers click on an item PurchaseItem(itemID): used during purchase flow What’s a good place to look for a vuln? Wild bug 2: (commerce)

32 Flaw: Access controls didn’t verify itemID is tied to the authenticated user (only enforced by UI) Impact: Shop for free Wild bug 2: (commerce)

33 Administrative page (internal) could monitor usage statistics through a web application Heaviest users (username and actual name) Load of services Wild bug 3: (server monitor)

34 Flaw 1: Actual name wasn’t sanitized when gathering statistics (only the username is sanitized) Actual name reappeared on the monitor page Try to inject code on the admin page Wild bug 3: (server monitor)

35 Challenge 1: must create a valid JSON object (a quoted string name/value pair object) Challenge 2: can’t use capitalized characters Challenge 3: do something awesome Wild bug 3: (server monitor)

36 Challenge 1: must create a valid JSON object (a quoted string name/value pair object) Challenge 2: can’t use capitalized characters Challenge 3: do something awesome Flaw 2: CSRF (doing an action as the logged in admin) Actual Name: \" onmouseover=\"$.get(‘ ')\" Wild bug 3: (server monitor)

37 Flaws: Tried to ignore actual name, but added it back in Relied on insufficient input filtering and output encoding Exploited the application’s vulnerability to CSRF Impact: bridging the gap into the intranet Vulnerabilities often need to be combined before exploit Wild bug 3: (server monitor)

38 void attachSuffix(char *userinputprefix, size_t inputSize) { char *withSuffix; withSuffix = malloc(inputSize + 2); if (withSuffix == NULL) { //meh, don’t care that much return; } memcpy(withSuffix, userinputprefix, inputSize); withSuffix[inputSize] = ‘.’; withSuffix[inputSize + 1] = ‘\n’; … } Wild bug 4: (operating system)

39 Flaw: Integer overflow into heap overflow Impact: memory corruption or potential code execution Wild bug 4: (operating system)

40 Some crazy person decided there should be double spaces after periods*. Pseudo-Code: Loop through the text byte by byte. If a period and a single space (followed by a non-space character) is encountered in an text, do the following: 1. Allocate a larger buffer if there isn’t room in the existing one (custom memory management) 2. memmove() the buffer following the “. “ one byte over 3. Write an additional space character in the vacated spot 4. Loop back to #1 until entire text is processed * That person is terrible and enforcing “grammar rules” from the age of typewriters. Wild bug 5: (forum text parser)

41 What’s the worst case runtime for parsing a text? Wild bug 5: (forum text parser)

42 What’s the worst case runtime for parsing a text? O(n^2) What happens if you send in a text of only “. “? Wild bug 5: (forum text parser)

43 What’s the worst case runtime for parsing a text? O(n^2) What happens if you send in a text of only “. “? DoS (asymmetric effort between attacker and server) Wild bug 5: (forum text parser)

44 Bug Finding as Warfare

45 Innovations in warfare always decrease the cost for later adopters. The Trickle Down Effect

46

47 How about with cyber warfare? Mid-2000’s Nation State APT: Spear-phish Exploit tied to intelligence on AV Active Directory attacks to spread horizontally Access production data via internal interfaces The Trickle Down Effect

48 Well, maybe not that scary…

49 Most public example of an “Advanced Persistent Threat” Advanced = 0-day custom malware Persistent = Slow and careful, non-financially motivated Hit at least 35 US companies in , five are clients Operation Aurora

50 Aurora Attack Code function window :: onload () { var SourceElement = document.createElement ("div"); document.body.appendChild (SourceElement); var SavedEvent = null; SourceElement.onclick = function () { SavedEvent = document.createEventObject (event); document.body.removeChild (event.srcElement); } SourceElement.fireEvent ("onclick"); SourceElement = SavedEvent.srcElement; }

51 Use after free vulnerability (MS – Remote Code Execution in IE 5-8) Memory typically has a reference counter (how many people have a handle to me?) Improper reference counter allowed Javascript to still reference a function in a freed block of memory Free memory Heap spray attack code (likely it gets written to the freed block because of how IE memory management works) Call function Fairly reliable code execution Operation Aurora

52 Heap block function window :: onload () { var SourceElement = document.createElement ("div"); document.body.appendChild (SourceElement); var SavedEvent = null; SourceElement.onclick = function () { SavedEvent = document.createEventObject (event); document.body.removeChild (event.srcElement); } SourceElement.fireEvent ("onclick"); SourceElement = SavedEvent.srcElement; }

53 Operation Aurora Heap block function window :: onload () { var SourceElement = document.createElement ("div"); document.body.appendChild (SourceElement); var SavedEvent = null; SourceElement.onclick = function () { SavedEvent = document.createEventObject (event); document.body.removeChild (event.srcElement); } SourceElement.fireEvent ("onclick"); SourceElement = SavedEvent.srcElement; }

54 Heap Spray! Create a bunch of elements with attack code and then free them (attack code gets written to lots of heap blocks) IE Small Block Manager Reuses memory pages Call the event pointing to freed memory Code execution! Operation Aurora Attack code

55 Valuable exploit! How was it used? Social Engineering (get someone to click a link), almost always the weakest link Escalate privileges (cached credentials) Spread (Active Directory, brute force attack) Gather (source code, financial data) Exfiltration (to China, out of intranet on Christmas) Operation Aurora

56 Advanced Persistent Threat Advanced attackers with talent (zero days) and time (months or years) Targeted attacks (not just going after the vulnerable) Non-traditional attacks, likely hard to monetize Whodunit? Operation Aurora

57 [ worm [ rootkit [ rootkit [ sabotage ] ] ] ] Five zero-day vulnerabilities Two stolen certificates Almost surgically targeted Eight propagation methods Partridge in a malware pear tree Stuxnet

58 Mixed MS Windows environment = Redundant Not exploiting memory corruption = Reliable Target: Iranian air-gapped networks operating centrifuges to enrich nuclear material (Natanz) How can you get a foot in the door? USB keys The Target

59 Zero-Day* Vulnerabilities: MS (Shell LNK / Shortcut) MS (Print Spooler Service) MS (Win32K Keyboard Layout) MS (NetPathCanonicalize()), (Patched) MS (Task Scheduler) CVE (Siemens SIMATIC Static Password) USB Vulnerability

60 You know, shortcuts and such Where does the icon come from? Loaded from a CPL (Control Panel File) specified by the user A CPL is just a DLL USB keys have attack DLL and a shortcut referencing the DLL Plugging in the USB stick leads to arbitrary code execution MS (Shell LNK/Shortcut)

61 Flaw: we should run a user-specified DLL to display an icon for a shortcut?! Pop Quiz: Which techniques that we have discussed could lead to discovery of this flaw? A) Fuzzing B) Disassembly C) Debugging D) BinDiff MS (Shell LNK/Shortcut)

62 I Love Security, What’s Next? Ethics in security Possible Careers

63 Ethics in Security Big ethical debates used to be: Responsible vs Full Disclosure

64 Ethics in Security Big ethical debates used to be: Responsible vs Full Disclosure Debate has shifted to: Disclosure vs Selling Weapons

65 Careers in Security Shape your job around your ethical standpoint, not vice versa

66 Careers in Security Shape your job around your ethical standpoint, not vice versa Write security relevant software

67 Careers in Security Shape your job around your ethical standpoint, not vice versa Write security relevant software Write (more) secure software

68 Careers in Security Shape your job around your ethical standpoint, not vice versa Write security relevant software Write (more) secure software Be a criminal

69 Careers in Security Shape your job around your ethical standpoint, not vice versa Write security relevant software Write (more) secure software Be a criminal Academia

70 Careers in Security Shape your job around your ethical standpoint, not vice versa Write security relevant software Write (more) secure software Be a criminal Academia Pen testing!

71 Go into a big company blindly Start your own company and think this is going to happen What not to do…

72 Always go into a meeting knowing what you want the outcome to be Ask for a small raise after an offer Common Stock is for Commoners Be part of the product, not the plumbing Career Tips

73 @alexstamos Questions?


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